From: David Laight <david.laight.linux@gmail•com>
To: Ryan Roberts <ryan.roberts@arm•com>
Cc: "Jason A. Donenfeld" <Jason@zx2c4•com>,
Catalin Marinas <catalin.marinas@arm•com>,
Will Deacon <will@kernel•org>,
Huacai Chen <chenhuacai@kernel•org>,
Madhavan Srinivasan <maddy@linux•ibm.com>,
Michael Ellerman <mpe@ellerman•id.au>,
Paul Walmsley <pjw@kernel•org>,
Palmer Dabbelt <palmer@dabbelt•com>,
Albert Ou <aou@eecs•berkeley.edu>,
Heiko Carstens <hca@linux•ibm.com>,
Vasily Gorbik <gor@linux•ibm.com>,
Alexander Gordeev <agordeev@linux•ibm.com>,
Thomas Gleixner <tglx@linutronix•de>,
Ingo Molnar <mingo@redhat•com>, Borislav Petkov <bp@alien8•de>,
Dave Hansen <dave.hansen@linux•intel.com>,
Kees Cook <kees@kernel•org>,
"Gustavo A. R. Silva" <gustavoars@kernel•org>,
Arnd Bergmann <arnd@arndb•de>,
Mark Rutland <mark.rutland@arm•com>,
Ard Biesheuvel <ardb@kernel•org>,
Jeremy Linton <jeremy.linton@arm•com>,
linux-kernel@vger•kernel.org,
linux-arm-kernel@lists•infradead.org, loongarch@lists•linux.dev,
linuxppc-dev@lists•ozlabs.org, linux-riscv@lists•infradead.org,
linux-s390@vger•kernel.org, linux-hardening@vger•kernel.org
Subject: Re: [PATCH v4 2/3] prandom: Add __always_inline version of prandom_u32_state()
Date: Wed, 28 Jan 2026 18:32:51 +0000 [thread overview]
Message-ID: <20260128183251.7177c345@pumpkin> (raw)
In-Reply-To: <670c2b78-02e2-4617-80d9-3c896077f02a@arm.com>
On Wed, 28 Jan 2026 17:33:19 +0000
Ryan Roberts <ryan.roberts@arm•com> wrote:
> On 28/01/2026 17:00, Jason A. Donenfeld wrote:
> > On Mon, Jan 19, 2026 at 01:01:09PM +0000, Ryan Roberts wrote:
> >> We will shortly use prandom_u32_state() to implement kstack offset
> >> randomization and some arches need to call it from non-instrumentable
> >> context. So let's implement prandom_u32_state() as an out-of-line
> >> wrapper around a new __always_inline prandom_u32_state_inline(). kstack
> >> offset randomization will use this new version.
> >>
> >> Acked-by: Mark Rutland <mark.rutland@arm•com>
> >> Signed-off-by: Ryan Roberts <ryan.roberts@arm•com>
> >> ---
> >> include/linux/prandom.h | 20 ++++++++++++++++++++
> >> lib/random32.c | 8 +-------
> >> 2 files changed, 21 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/include/linux/prandom.h b/include/linux/prandom.h
> >> index ff7dcc3fa105..801188680a29 100644
> >> --- a/include/linux/prandom.h
> >> +++ b/include/linux/prandom.h
> >> @@ -17,6 +17,26 @@ struct rnd_state {
> >> __u32 s1, s2, s3, s4;
> >> };
> >>
> >> +/**
> >> + * prandom_u32_state_inline - seeded pseudo-random number generator.
> >> + * @state: pointer to state structure holding seeded state.
> >> + *
> >> + * This is used for pseudo-randomness with no outside seeding.
> >> + * For more random results, use get_random_u32().
> >> + * For use only where the out-of-line version, prandom_u32_state(), cannot be
> >> + * used (e.g. noinstr code).
If you are going to respin:
(e.g. noinst or performance critical code).
David
> >> + */
> >> +static __always_inline u32 prandom_u32_state_inline(struct rnd_state *state)
> >
> > This is pretty bikesheddy and I'm not really entirely convinced that my
> > intuition is correct here, but I thought I should at least ask. Do you
> > think this would be better called __prandom_u32_state(), where the "__"
> > is kind of a, "don't use this directly unless you know what you're doing
> > because it's sort of internal"? It seems like either we make this inline
> > for everybody, or if there's a good reason for having most users use the
> > non-inline version, then we should be careful that new users don't use
> > the inline version. I was thinking the __ would help with that.
>
> I'm certainly happy to do that, if that's your preference. I have to respin this
> anyway, given the noinstr issue.
>
> >
> > Jason
>
next prev parent reply other threads:[~2026-01-28 18:33 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-19 13:01 [PATCH v4 0/3] Fix bugs and performance of kstack offset randomisation Ryan Roberts
2026-01-19 13:01 ` [PATCH v4 1/3] randomize_kstack: Maintain kstack_offset per task Ryan Roberts
2026-01-19 16:10 ` Dave Hansen
2026-01-19 16:51 ` Ryan Roberts
2026-01-19 16:53 ` Dave Hansen
2026-01-19 13:01 ` [PATCH v4 2/3] prandom: Add __always_inline version of prandom_u32_state() Ryan Roberts
2026-01-28 17:00 ` Jason A. Donenfeld
2026-01-28 17:33 ` Ryan Roberts
2026-01-28 18:32 ` David Laight [this message]
2026-01-30 16:16 ` Christophe Leroy (CS GROUP)
2026-01-19 13:01 ` [PATCH v4 3/3] randomize_kstack: Unify random source across arches Ryan Roberts
2026-01-20 23:50 ` kernel test robot
2026-01-21 10:20 ` David Laight
2026-01-21 14:48 ` David Laight
2026-01-21 10:52 ` Ryan Roberts
2026-01-21 12:32 ` Mark Rutland
2026-02-18 15:20 ` Ryan Roberts
2026-02-22 21:34 ` Thomas Gleixner
2026-02-23 9:41 ` David Laight
2026-03-03 14:43 ` Ryan Roberts
2026-01-19 16:00 ` [PATCH v4 0/3] Fix bugs and performance of kstack offset randomisation Dave Hansen
2026-01-19 16:44 ` Kees Cook
2026-01-19 16:51 ` Dave Hansen
2026-01-20 16:32 ` Ryan Roberts
2026-01-20 16:37 ` Dave Hansen
2026-01-20 16:45 ` Ryan Roberts
2026-01-20 18:45 ` David Laight
2026-01-19 16:25 ` Heiko Carstens
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